Sibling age differences and autism

Children who are born closer in age to their older siblings may have an increased risk of being diagnosed with autism. Researchers from Columbia University in New York studied more than 600,000 pairs of siblings born in California between 1992 and 2002. In 3,000 of these pairs the older child had not been diagnosed with autism while the younger one had. In sibling pairs where the mother became pregnant with her second child less than a year after giving birth to her first 7.5 out of 1,000 younger children were diagnosed with autism but where the gap was three years or more only 2.5 out of every 1,000 were. The shorter the age gap between children the greater the risk of developing autism. The researchers thought that this could either be because women's nutrition and stress levels had not recovered properly after giving birth to their first child by the time they became pregnant again or because, having seen normal childhood development relatively recently, the parents were quicker to spot abnormal development in their younger child.